Heretofore, a position adjusting device for a steering wheel has been used for changing the height position or longitudinal position of a steering wheel according to the physical attribute of the body of a driver, the driving posture of the driver, and the like. In general, as such a position adjusting device, there has been used a structure in which a frictional force between a fixed side bracket supported and fixed on the vehicle body side and a displacement side bracket set on the steering column side is adjusted. That is to say, when adjusting the position of the steering wheel, an adjusting lever is operated in a predetermined direction to thereby reduce the frictional force acting between both of the above brackets. On the other hand, when holding the position of the steering wheel at a post-adjustment position, the adjusting lever is operated in a direction opposite to the predetermined direction, to thereby increase the frictional force. In the case of such a structure, it is preferable that the friction area is increased in order to increase the force for holding the position of the steering wheel at the post-adjustment position without increasing the operating amount or operating force of the adjusting lever. Taking such circumstances into consideration, Patent Documents 1 and 2 disclose structures in which a plurality of friction members is superposed to thereby increase the friction area.
FIG. 6 and FIG. 7 show an example of such a position adjusting device for a steering wheel wherein a plurality of friction members is used to thereby increase the friction area, so that the force for holding the position of a steering wheel (1) at the post-adjustment position is increased. This structure enables adjustment of the vertical and longitudinal position of the steering wheel (1).
The steering wheel (1) is supported and fixed on the rear end section (upper end section) of a steering shaft (2) provided in a state of being inclined in an upward direction towards the rear side (right side in FIG. 6). This steering shaft (2) is such that the front end section of an outer shaft (3) provided on the rear half section (right half section in FIG. 6) is spline-engaged with the rear end section of an inner shaft (4) provided on the front half section (left half section in FIG. 6), to thereby enable adjustment of the longitudinal position of the outer shaft (3). Such a steering shaft (2) is supported, while only being allowed to rotate, with roller bearings (8a, 8b, 8c) such as deep groove ball bearings (in a state where axial displacement with respect to the steering column (7) is blocked), on the inside of a steering column (7) formed with an outer column (5) and an inner column (6) combined telescopically (extendably and retractably).
Moreover, in the example shown in the drawings, there is installed an electric power steering device that applies an auxiliary steering force to the steering shaft (2) using an electric motor. Therefore an electric motor is fixed in a housing (9) fixed on the front end section of the steering column (7), and there is installed a gear transmission mechanism for transmitting the output of the electric motor to the steering shaft (2). The structure of the electric power steering device has been widely known heretofore and is not a key issue of the present invention (the present invention can be practiced regardless of the presence or structure of the power steering device), and the detailed description thereof is therefore omitted. The housing (9) is, via a cross shaft (10) and oscillating bracket (11), swingably supported on one portion of a vehicle body. Moreover, the portion at the front end section of the steering shaft (2) that projects from the housing (9) is connected to an intermediate shaft (13) via a universal coupling (12). This intermediate shaft (13) is also such that the entire length thereof can be extended and retracted with a spline engagement section provided in an intermediate section thereof, and displacement of the universal coupling (12) in the longitudinal direction due to oscillating of the steering column (7) can be absorbed.
With the above configuration, it is possible to adjust the height position of the steering wheel (1) based on oscillating displacement about the cross shaft (10), and it is possible to adjust the longitudinal position of the steering wheel (1) based on the telescopic motion of the steering shaft (2) and the steering column (7). In order to fix the position of this steering wheel (1) at a post adjustment position, a displacement side bracket (14) is set on a part of the steering column (7) and a fixed side bracket (15) is fixed on the vehicle body side. Both of these brackets (14) and (15) can be freely engaged with or disengaged from each other with operation of a position adjusting lever (16). The front end section of the intermediate shaft (13) is connected, via another universal coupling, to a steering gear input shaft (not shown in the drawing), so that desired angles can be given to wheels to be steered (front wheels in general) based on the rotation of this intermediate shaft (13).
In the example shown in the drawing, the displacement side bracket (14) is provided integrally with the outer column (5) in the front end side portion of the bottom face of this outer column (5) that is an aluminum alloy casting (including a die cast molded product) and that constitutes the steering column (7). Also, in the displacement side bracket (14), there is formed, in a state of passing through the displacement side bracket (14) in the left-right direction (transverse direction), a longitudinal elongated hole (18), which is elongate in the longitudinal direction, for inserting a tension rod (17) as a rod member therethrough.
Moreover, the fixed side bracket (15) is formed such that an upper side bracket element (19) and a lower side bracket element (20) respectively bent-formed with metal plates are join-fixed by means of welding. The upper side bracket element (19) is to support and fix the fixed side bracket (15) on the vehicle body side, and has a pair of left and right attachment plate sections (21). With the structure commonly known in the technical field of a steering wheel device for a vehicle, both of these attachment plate sections (21) are supported and fixed on the vehicle body side while being allowed to come away forward in the case of a secondary collision.
Moreover, the lower side bracket element (20) has a pair of supporting plate sections (22) respectively extending down in the vertical direction from the bottom face of the upper side bracket element (19). A gap D between the inner faces (side faces opposing each other) of both of these supporting plate sections (22) substantially matches a gap W between the outer faces of the displacement side bracket (14) (width of the displacement side bracket (14)) (D≈W). In each position of both of the above supporting plate sections (22) which align with each other, there is formed a vertical elongated hole (23) for inserting the tension rod (17) therethrough (that is preferably of an arc shape about the cross shaft (10)) that is elongate in the vertical direction. On each outer face portion of both of the supporting plate sections (22), there is arranged a plurality of first friction plates (24) and a plurality of second friction plates (25).
Among these first and second friction plates (24, 25), in the first friction plates (24) arranged in the vertical direction along the outer faces of both of these supporting plate sections (22), there is respectively formed a first elongated hole (26) that aligns with the vertical elongated hole (23) formed in both of these supporting plate sections (22). The upper end section of each first friction plate (24) respectively having such a configuration is joined and supported on the upper end section outer face of both of the supporting plate sections (22) with a first set screw (27). Therefore, each first friction plate (24) does not displace in the vertical direction.
On the other hand, in the second friction plates (25) arranged in the longitudinal direction along the displacement side bracket (14), there is respectively formed a second elongated hole (28) that aligns with the longitudinal elongated hole (18) formed in the displacement side bracket (14). The front end section of each second friction plate (25) respectively having such a configuration is joined and supported on the front end section outer face of the displacement side bracket (14) with a second set screw (29). Therefore, each second friction plate (25) does not displace in the longitudinal direction. Each of such second friction plates (25) and each of the first friction plates (24) are arranged on the outer face of both of these supporting plate sections (22) in a state of being alternately superposed.
Moreover, the tension rod (17) is inserted through; the longitudinal elongated hole (18), both of the vertical elongated holes (23), and the respective first and second elongated holes (26, 28). This tension rod (17) has an outward flange shaped flange section (30) formed on the base end section thereof (right end section in FIG. 7), and an engagement section (32) formed on the base end side portion of a rod section (31) is engaged with one of the vertical elongated holes (23) which is on one side (the right side in FIG. 7) while only allowing itself free displacement (elevation) along this vertical elongated hole (23). Consequently, the sectional shape of the engagement section (32) is of a non-circular shape such as oval shape having a straight line portion that comes in sliding contact with the inner edge of the vertical elongated hole (23), but that blocks rotation inside this vertical elongated hole (23).
On the other hand, a pressing plate (33) is externally fitted onto a portion of the tip end side portion of the intermediate section of the rod section (31), which projects from the supporting plate section (22) which is on the other side (the left side in FIG. 7) and the respective first and second friction plates (24, 25) arranged on the outer face portion of this supporting plate section (22), and there is also provided a cam mechanism (34) for the purpose of pressing thereto. This cam mechanism (34) and the tension rod (17) form a pressing device. This cam mechanism (34) is one that has a structure widely known in the technical field of a steering wheel device for a vehicle, and has a structure that allows an axial dimension T to increase and decrease based on the operation of the position adjusting lever (16). In the state where this position adjusting lever (16) has been turned in a predetermined direction and the axial dimension T has been thereby increased, the distance between the one side face of the pressing plate (33) and the inner face of the flange section (30) is reduced to thereby increase a frictional force that is present between both of these faces and that acts between the opposing faces that are friction-engaged with each other.
That is to say, in this state: the contact pressure between both side faces of the displacement side bracket (14) and the inner faces of both of the supporting plate sections (22); the contact pressure between the outer faces of both of these supporting plate sections (22) and the inner face of the innermost second friction plate (25); the contact pressure between the side faces of the respective first and second friction plates (24, 25) adjacent to each other; and the contact pressure between the outer face of the outermost first friction plate (24) and one side face of the pressing plate (33) or the inner face of the flange section (30), all increase. In this state, the total sum of the frictional forces that act between the respective frictional engagement sections becomes sufficiently large. As a result, it is possible to sufficiently increase the supporting strength of the displacement side bracket (14) with respect to the fixed side bracket (15), while maintaining the position of the steering wheel (1) in the same state with a sufficiently large strength.
On the other hand, when adjusting the position of the steering wheel (1), the position adjusting lever (16) is turned in the direction opposite to the above predetermined direction, to thereby reduce the axial dimension T and increase the distance between the one side face of the pressing plate (33) and the inner face of the flange section (30). In this state, the frictional force that is present between both of these faces and that acts between the opposing faces that are friction-engaged with each other is reduced or lost, and it becomes possible to adjust the displacement side bracket (14) with respect to the fixed side bracket (15), in the vertical and longitudinal directions. Accordingly, having adjusted the position of the steering wheel (1) to a desired position in this state, the position adjusting lever (16) is turned in the predetermined direction. As a result, the position of the steering wheel (1) is held at the desired position.
In the case of the structure shown in FIG. 6 and FIG. 7, the respective first and second friction plates (24, 25) are arranged outside of the pair of supporting plate sections (22) that constitute the fixed side bracket (15). Each of the friction plates (24, 25) is respectively of a thin plate shape with a low level of rigidity, and can be easily deformed based on interference (abutment) with other members existing therearound. In the case of being deformed, even in a state where the position adjusting lever (16) has been turned in the predetermined direction, a desired frictional force cannot be generated in the contact portion between the respective friction plates (24, 25), so that the force for maintaining the steering wheel (1) at the desired position may become weaker. Moreover, still there is a possibility of injuries to the driver if part of the body of the driver such as the knee collides with an end edge of any one of the friction plates (24, 25) in the event of a collision accident or the like.
In the case of the conventional structure shown in FIG. 6 and FIG. 7, a plurality of independent flat first and second friction plates (24, 25) are respectively provided for each outer face portion of both of the supporting plate sections (22). That is to say, in the example shown in the drawings, two of each of the friction plates (24, 25) being four in total, are provided for each outer face portion of each supporting plate section (22), meaning a total of eight friction plates are provided therefor. The respective end sections of these friction plates (24, 25) are supported on both of the supporting plate sections (22) (fixed side bracket (15)) or on the displacement side bracket (14) with the first and second set screws (27, 29). However, until the tension rod (17) has been inserted into the first and second elongated holes (26, 28), the respective friction plates (24, 25) can oscillate or turn about the first and second set screws (27, 29).
When assembling the position adjusting device for a steering wheel, the tension rod (17) needs to be inserted not only through the longitudinal and vertical elongated holes (18, 23), but also through the respective first and second elongated holes (26, 28). When carrying out such an insertion operation, these respective first and second elongated holes (26, 28) need to be aligned. However, if the respective friction plates (24, 25) independently oscillate or turn, then such an alignment operation needs to be carried out for the respective friction plates (24, 25), increasing the operational burden. As a result, it becomes an obstacle to assembly operation efficiency of the position adjusting device for a steering wheel, making it more difficult to achieve a cost reduction in this position adjusting device for a steering wheel. Patent Document 2 discloses a structure in which the base end sections of a plurality of friction plates are superposed via spacers, and the base end section of each friction plate and the spacer are fixed by means of welding. However in the case of such a structure disclosed in Patent Document 2, it is necessary to carry out a welding operation in a state where the spacers and the base end sections of the respective friction plates are appropriately superposed, and therefore the operational burden in manufacturing is significant and a cost reduction cannot be easily achieved.    Patent Document 1: Japanese Patent Application Publication No. H10-35511    Patent Document 2: Japanese Utility Model Publication No. S62-19483